Question

Verify :
Cos (a+b) = (cos a cos b) - (sin a sin b)

(a=30 and b=60)

Answer 1

cos(30+60)=cos90=0
cos30cos60-sin30sin60
√3/2(1/2)-1/2(√3/2)
√3/4-√3/4=0

so cos(a+b)=cosa cosb -sina sinb

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Answer 2

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